Late Pleistocene-Holocene landscape evolution in the lower Peixe river, Brazil: A meandering river valley

Abstract

This study investigated the lower terrace and floodplain formation in the lower Peixe River in southeastern Brazil. Morphologic, sedimentologic and geochronologic analyses in this meandering tributary of the Parana River allowed an integrated approach to reconstructing fluvial changes from the late Pleistocene. Geomorphic units were mapped with Global Navigation Satellite System, satellite imagery and digital surface model interpretation, and sedimentary facies and radiocarbon (C-14) dating analyses were performed on palaeochannels and backswamps. The palaeochannels on the lower terrace indicate fluvial activity during the late Pleistocene, torrential flows during the Northgrippian stage, and abandonments during the Meghalayan stage. The back-swamp evaluated on the lower terrace documents the depositional change from oxbow lake abandonment in the Greenlandian stage to tributary flow, which passes flows over the palaeodrainage during flood episodes, while another back-swamp in the floodplain highlights an intense morphodynamic removal of terrace deposits. An incisive phase during the Meghalayan stage is the main event responsible for establishing the current fluvial landscape, which promotes the formation of the lower terrace and floodplain. Local variations (i.e., tributary flows) in the degradation process on the terraces results in a topographical and morphological contrast between corresponding geochronologic units. Therefore, adjustment stages in the fluvial relief drive wetland variability in the fill terraces, which are fundamental to understanding degradational processes and formulating environmental management policies.